As they age, most dogs will develop a lump or bump, or a whole series of them. It can be tempting to ignore them, or to write them off as just another old-dog thing. While that’s what they often are, they should always be checked out by your veterinarian. Canine mast cell tumors are one of the five cancers most frequently diagnosed in dogs.
What is it?
Part of the immune system, mast cells’ job is to respond to inflammation and allergic reactions. Among other things, mast cells contain granules of histamine, which are released in allergic/hypersensitivity reactions (think hay fever). They are found in connective tissues, particularly those close to the surface. When mast cells proliferate at a tissue site, a tumor may result.
Accounting for about 20 percent of all skin tumors, mast cell tumors can be locally invasive, which sometimes makes them difficult to remove completely.
via Whisker Therapy